Research has been carried out into two aspects of the cerebral circulation: (1) Its neurogenic control and (2) the basis of cerebral vasospasm. Since small cerebral blood vessels may be quantitatively more important in the regulation of blood flow than larger vessels, our studies on the basilar artery have been extended to vessels as small as 100 micron O.D. An analysis of the adrenergic neuroeffector mechanism in these small vessels suggests that their main characteristics are similar to those of larger cerebral vessels. An analysis is being carried out of the pathophysiology of cerebral vasospasm using two models. The first is the stretched rabbit basilar artery where in association with small discrete tears of the internal elastic lamina there is local prolonged constriction and second, the vasospasm associated with subarachnoid hemorrhage in the monkey. This study involves both functional analysis of nerve and muscle together with a morphological survey. The increasing evidence for nonuniform regional changes in cerebral blood flow has prompted the study of a possible role of cushions and nerve collars in the regulation of flow in the circulation. Our general conclusion is that cushions are inconstant in position and that certain observation of adrenergic nerve collars may be artifactual. Thus it is concluded that nonuniform alterations of cerebral blood flow cannot be accounted for by these factors. BIBLIOGRAPHIC REFERENCES: Bevan, J.A., Duckles, S.P. and Lee, T.J-F.: Histamine potentiation of nerve- and drug-induced responses of a rabbit cerebral artery. Circ. Res. 36:647-653, 1975. Bevan, J.A. and Bevan, R.D.: Preliminary analysis of the neurogenic vasoconstriction of basilar artery. Chapter in Cerebral Circulation and Metabolism, ed. by Thomas W. Langfitt, Lawrence C. McHenry, Jr., Martin Reivich, and Harry Wollman. pp. 494-496, Springer-Verlag, New York, 1975.